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/* nettle, low-level cryptographics library
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* Copyright (C) 2013 Niels Möller
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* The nettle library is free software; you can redistribute it and/or modify
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* it under the terms of the GNU Lesser General Public License as published by
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* the Free Software Foundation; either version 2.1 of the License, or (at your
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* option) any later version.
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* The nettle library is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
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* License for more details.
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* You should have received a copy of the GNU Lesser General Public License
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* along with the nettle library; see the file COPYING.LIB. If not, write to
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* the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
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/* Development of Nettle's ECC support was funded by the .SE Internet Fund. */
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#include "ecc-internal.h"
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ecc_mul_g_itch (const struct ecc_curve *ecc)
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/* Needs 3*ecc->size + scratch for ecc_add_jja. */
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return ECC_MUL_G_ITCH (ecc->size);
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ecc_mul_g (const struct ecc_curve *ecc, mp_limb_t *r,
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const mp_limb_t *np, mp_limb_t *scratch)
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/* Scratch need determined by the ecc_add_jja call. Current total is
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9 * ecc->size, at most 648 bytes. */
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#define scratch_out (scratch + 3*ecc->size)
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bit_rows = (ecc->bit_size + k - 1) / k;
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mpn_zero (r, 3*ecc->size);
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for (i = k, is_zero = 1; i-- > 0; )
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ecc_dup_jj (ecc, r, r, scratch);
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for (j = 0; j * c < bit_rows; j++)
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/* Avoid the mp_bitcnt_t type for compatibility with older GMP
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/* Extract c bits from n, stride k, starting at i + kcj,
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ending at i + k (cj + c - 1)*/
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for (bits = 0, bit_index = i + k*(c*j+c); bit_index > i + k*c*j; )
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limb_index = bit_index / GMP_NUMB_BITS;
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if (limb_index >= ecc->size)
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shift = bit_index % GMP_NUMB_BITS;
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bits = (bits << 1) | ((np[limb_index] >> shift) & 1);
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sec_tabselect (tp, 2*ecc->size,
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+ (2*ecc->size * (mp_size_t) j << c)),
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cnd_copy (is_zero, r, tp, 2*ecc->size);
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cnd_copy (is_zero, r + 2*ecc->size, ecc->unit, ecc->size);
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ecc_add_jja (ecc, tp, r, tp, scratch_out);
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/* Use the sum when valid. ecc_add_jja produced garbage if
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is_zero != 0 or bits == 0, . */
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cnd_copy (bits & (is_zero - 1), r, tp, 3*ecc->size);
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is_zero &= (bits == 0);